System and Method to Align and Measure Alignment Patterns on Multiple Layers

ABSTRACT

A system and method are used to increase alignment accuracy of feature patterns through detection of alignment patterns on both a surface layer and at least one below surface layers of an object. A first frequency of light, such as visible light, is used to detect alignment patterns on the surface layer and a second frequency of light, such as infrared light, is used to detect patterns one layer below the surface. For example, reflected light of a first frequency and transmitted light of a second frequency are co-focused onto detector after impinging on respective alignment patterns. The co-focused light is then used to determine proper alignment of the object for subsequent pattern features. This substantially increases accuracy of alignment of pattern features between layers, as compared to conventional systems.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Non-Provisional ApplicationNo. 11/272,711, filed Nov. 15, 2005, which will issue as U.S. Pat. No.7,365,848 on Apr. 29, 2008, which claims benefit to U.S. ProvisionalApplication No. 60/631,991, filed Dec. 1, 2004, all of which areincorporated by reference herein in its entirety.

BACKGROUND

1. Field of the Invention

The present invention relates to a lithographic apparatus and a devicemanufacturing method.

2. Related Art

A lithographic apparatus is a machine that applies a desired patternonto a target portion of a substrate. The lithographic apparatus can beused, for example, in the manufacture of integrated circuits (ICs), flatpanel displays, and other devices involving fine structures. In aconventional lithographic apparatus, a patterning means, which isalternatively referred to as a mask or a reticle, can be used togenerate a circuit pattern corresponding to an individual layer of theIC (or other device), and this pattern can be imaged onto a targetportion (e.g., comprising part of one or several dies) on a substrate(e.g., a silicon wafer or glass plate) that has a layer ofradiation-sensitive material (e.g., resist). Instead of a mask, thepatterning means can comprise an array of individually controllableelements that generate the circuit pattern.

In general, a single substrate will contain a network of adjacent targetportions that are successively exposed. Known lithographic apparatusinclude steppers, in which each target portion is irradiated by exposingan entire pattern onto the target portion in one go, and scanners, inwhich each target portion is irradiated by scanning the pattern throughthe beam in a given direction (the “scanning” direction), whilesynchronously scanning the substrate parallel or anti-parallel to thisdirection.

As discussed above, a lithographic apparatus uses a patterning device topattern incoming light. A static patterning device can include reticlesor masks. A dynamic patterning device can include an array ofindividually controllable elements that generate a pattern throughreceipt of analog or digital signals.

Multiple layers can be formed on each substrate, with each layerreceiving feature patterns that interconnect within that layer and toother feature patterns in previous/subsequent layers. However, typicallyonly an alignment patterned formed on a top layer of the substrate isused to determine proper alignment of feature patterns with respect toeach other. With tolerances getting smaller, it would be desirable foralignment of subsequent feature patterns to utilize alignment patternson the top layer and one or more previously formed layers.

Therefore, what is needed is a system and method that allow formeasurement or detection of alignment patterns on a top layer and one ormore previously formed layers before forming a next feature pattern.

SUMMARY

According to one embodiment of the present invention, a system comprisesan alignment system including first and second light sources and adetector that generates a measured signal therefrom. The system furthercomprises an object, including a first layer including a first alignmentpattern, and a second layer including a second alignment pattern, thesecond layer being below the first layer. The system also included afocusing system that co-focuses on the detector light from the first andsecond light sources after each has impinged on the respective the firstand second alignment patterns. The system then aligns the object basedon the measured signal wherein the measured signal is generated from theco-focused light from the first and second alignment patterns.

According to one embodiment of the present invention, there is provideda method comprising the following steps. Generating at least a firstlight beam and a second light beam. Impinging the first light beam ontoa first alignment pattern on a first layer of an object. Focusing theimpinged first light beam onto a detector. Impinging the second lightbeam onto a second alignment pattern on a second layer of the object,the second layer of the object being below the first layer of theobject. Focusing the impinged second light beam onto the detector.Generating an alignment signal based on the detected first and secondalignment patterns; and aligning the object to receive a subsequentportion of a feature pattern based on the alignment signal.

Further embodiments and features of the present inventions, as well asthe structure and operation of the various embodiments of the presentinvention, are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form apartof the specification, illustrate embodiments of the present inventionand, together with the description, further serve to explain theprinciples of the invention and to enable a person skilled in thepertinent art to make and use the invention.

FIG. 1 depicts a lithographic apparatus, according to one embodiment ofthe invention.

FIGS. 2 and 3 show alignment systems, according to various embodimentsof the present invention.

FIGS. 4 and 5 show two optical devices that can be used in conjunctionwith each other in the alignment system of FIGS. 2 and 3, according toone embodiment of the present invention.

FIG. 6A shows an optical arrangement in a lithography system, accordingto one embodiment of the present invention.

FIG. 6B shows an IR portion of the optical arrangement in FIG. 6A,according to one embodiment of the present invention.

FIG. 7 shows a flowchart depicting a method, according to one embodimentof the present invention.

The present invention will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers mayindicate identical or functionally similar elements.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Overview

Although specific reference may be made in this text to the use of apatterning device in a lithographic system that patterns a substrate, itshould be understood that the patterning device described herein mayhave other applications, such as in a projector or a projection systemto pattern an object or display device (e.g., in a projection televisionsystem, or the like). Therefore, the use of the lithographic systemand/or substrate throughout this description is only to describe exampleembodiments of the present invention.

Embodiments of the present invention provide a system and method thatare used for alignment of feature patterns through detection ofalignment patterns on both a surface layer and at least one below (e.g.,buried) surface layers of an object. Visible light is used to detectalignment patterns on the surface layer and infrared light is used todetect patterns one layers below the surface. In this example, theobject is made from a material through which infrared light istransmitted and/or reflected and off of which visible light isreflected. For example, the object can be made from silicon. Thus,reflected visible light and transmitted or reflected infrared light areco-focused onto a detector. The co-focused light is then used todetermine proper alignment of the object for subsequent patternfeatures. This makes it possible to align pattern features between twolayers of alignment patterns or featured patterns when one of them isburied deeply and cannot be aligned by conventional alignment systems.

In one example, co-focusing is meant to describe when both the visibleand infrared light has a same focal length between a focusing system andthe detector. In one example, this can be accomplished through use of anoptical system. In another example, this can be accomplished through useof an optical system in conjunction with a positioning system that moveseither the object and/or the detector relative (e.g., towards/away) tothe optical system.

In one example of this description, visible light is within a range ofabout 540-600 nm, near infrared light is within a range of about650-1000 nm, and infrared light is within a wavelength of about1000-3500 nm, while 650-3500 are all referred to as infrared light.

Terminology

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as, for example, the manufacture of DNA chips,MEMS, MOEMS, integrated optical systems, guidance and detection patternsfor magnetic domain memories, flat panel displays, thin film magneticheads, micro and macro fluidic devices, etc. The skilled artisan willappreciate that, in the context of such alternative applications, anyuse of the terms “wafer” or “die” herein may be considered as synonymouswith the more general terms “substrate” or “target portion,”respectively.

The substrate referred to herein may be processed, before or afterexposure, in, for example, a track (a tool that typically applies alayer of resist to a substrate and develops the exposed resist) or ametrology or inspection tool. Where applicable, the disclosure hereinmay be applied to such and other substrate processing tools. Further,the substrate may be processed more than once, for example, in order tocreate a multi-layer IC, so that the term substrate used herein may alsorefer to a substrate that already contains multiple processed layers.

The term “array of individually controllable elements” as here employedshould be broadly interpreted as referring to any device that can beused to endow an incoming radiation beam with a patterned cross-section,so that a desired pattern can be created in a target portion of thesubstrate. The terms “light valve” and “Spatial Light Modulator” (SLM)can also be used in this context. Examples of such patterning devicesare discussed above and below.

A programmable mirror array may comprise a matrix-addressable surfacehaving a viscoelastic (i.e., a surface having appreciable and conjointviscous and elastic properties) control layer and a reflective surface.The basic principle behind such an apparatus is that, for example,addressed areas of the reflective surface reflect incident light asdiffracted light, whereas unaddressed areas reflect incident light asundiffracted light. The addressing can be binary or through multipleintermittent angles. Using an appropriate spatial filter, theundiffracted light can be filtered out of the reflected beam, leavingonly the diffracted light to reach the substrate. In this manner, thebeam becomes patterned according to the addressing pattern of thematrix-addressable surface.

It will be appreciated that, as an alternative, the filter may filterout the diffracted light, leaving the undiffracted light to reach thesubstrate. An array of diffractive optical micro electrical mechanicalsystem (MEMS) devices can also be used in a corresponding manner. Eachdiffractive optical MEMS device can include a plurality of reflectiveribbons that can be deformed relative to one another to form a gratingthat reflects incident light as diffracted light. This is sometimesreferred to as a grating light valve.

A further alternative embodiment can include a programmable mirror arrayemploying a matrix arrangement of tiny mirrors, each of which can beindividually tilted about an axis by applying a suitable localizedelectric field, or by employing piezoelectric actuation means. Onceagain, the mirrors are matrix-addressable, such that addressed mirrorswill reflect an incoming radiation beam in a different direction tounaddressed mirrors; in this manner, the reflected beam is patternedaccording to the addressing pattern of the matrix-addressable mirrors.The required matrix addressing can be performed using suitableelectronic means. In one example, groups of the mirrors can becoordinated together to be addresses as a single “pixel.” In thisexample, an optical element in an illumination system can form beams oflight, such that each beam falls on a respective group of mirrors.

In both of the situations described here above, the array ofindividually controllable elements can comprise one or more programmablemirror arrays.

A programmable LCD array can also be used.

It should be appreciated that where pre-biasing of features, opticalproximity correction features, phase variation techniques and multipleexposure techniques are used, for example, the pattern “displayed” onthe array of individually controllable elements may differ substantiallyfrom the pattern eventually transferred to a layer of or on thesubstrate. Similarly, the pattern eventually generated on the substratemay not correspond to the pattern formed at any one instant on the arrayof individually controllable elements. This may be the case in anarrangement in which the eventual pattern formed on each part of thesubstrate is built up over a given period of time or a given number ofexposures during which the pattern on the array of individuallycontrollable elements and/or the relative position of the substratechanges.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.,having a wavelength of 365, 248, 193, 157 or 126 nm) and extremeultra-violet (EUV) radiation (e.g., having a wavelength in the range of5-20 nm), as well as particle beams, such as ion beams or electronbeams.

In the lithography environment, the term “projection system” used hereinshould be broadly interpreted as encompassing various types ofprojection systems, including refractive optical systems, reflectiveoptical systems, and catadioptric optical systems, as appropriate, forexample, for the exposure radiation being used, or for other factorssuch as the use of an immersion fluid or the use of a vacuum. Any use ofthe term “lens” herein may be considered as synonymous with the moregeneral term “projection system.”

The illumination system may also encompass various types of opticalcomponents, including refractive, reflective, and catadioptric opticalcomponents for directing, shaping, or controlling the beam of radiation,and such components may also be referred to below, collectively orsingularly, as a “lens.”

The lithographic apparatus may be of a type having two (e.g., dualstage) or more substrate tables (and/or two or more mask tables). Insuch “multiple stage” machines the additional tables may be used inparallel, or preparatory steps may be carried out on one or more tableswhile one or more other tables are being used for exposure.

The lithographic apparatus may also be of a type wherein the substrateis immersed in a liquid having a relatively high refractive index (e.g.,water), so as to fill a space between the final element of theprojection system and the substrate. Immersion liquids may also beapplied to other spaces in the lithographic apparatus, for example,between the patterning device and the first element of the projectionsystem. Immersion techniques are well known in the art for increasingthe numerical aperture of projection systems.

Further, the apparatus may be provided with a fluid processing cell toallow interactions between a fluid and irradiated parts of the substrate(e.g., to selectively attach chemicals to the substrate or toselectively modify the surface structure of the substrate).

Exemplary Environment for a Patterning Device

Although the patterning device of the present invention can be used inmany different environments, as discussed above, a lithographicenvironment will be used in the description below. This is forillustrative purposes only.

A lithographic apparatus is a machine that applies a desired patternonto a target portion of an object. The lithographic apparatus can beused, for example, to pattern an object in a biotechnology environment,in the manufacture of ICs, flat panel displays, micro or nano fluidicdevices, and other devices involving fine structures. In an IC-basedlithographic environment, the patterning device is used to generate acircuit pattern corresponding to an individual layer of the IC (or otherdevice), and this pattern can be imaged onto a target portion (e.g.,comprising part of one or several dies) on a substrate (e.g., a siliconwafer or glass plate) that has a layer of radiation-sensitive material(e.g., resist). As discussed above, instead of a mask, in maskless IClithography the patterning device may comprise an array of individuallycontrollable elements that generate the circuit pattern.

In general, a single substrate will contain a network of adjacent targetportions that are successively exposed. Known lithographic apparatusinclude steppers, in which each target portion is irradiated by exposingan entire pattern onto the target portion in one go, and scanners, inwhich each target portion is irradiated by scanning the pattern throughthe beam in a given direction (the “scanning” direction), whilesynchronously scanning the substrate parallel or anti-parallel to thisdirection. These concepts will be discussed in more detail below.

FIG. 1 schematically depicts a lithographic projection apparatus 100,according to one embodiment of the invention. Apparatus 100 includes atleast a radiation system 102, a patterning device 104 (e.g., a staticdevice or an array of individually controllable elements), an objecttable 106 (e.g., a substrate table), and a projection system (“lens”)108.

Radiation system 102 is used to supply a beam 110 of radiation, which inthis example also comprises a radiation source 112.

Array of individually controllable elements 104 (e.g., a programmablemirror array) is used to pattern beam 110. In one example, the positionof the array of individually controllable elements 104 is fixed relativeto projection system 108. However, in another example, array ofindividually controllable elements 104 is connected to a positioningdevice (not shown) that positions it with respect to projection system108. In the example shown, each element in the array of individuallycontrollable elements 104 are of a reflective type (e.g., have areflective array of individually controllable elements).

Object table 106 is provided with an object holder (not specificallyshown) for holding an object 114 (e.g., a resist coated silicon wafer, aglass substrate, or the like). In one example, substrate table 106 isconnected to a positioning device 116 for accurately positioningsubstrate 114 with respect to projection system 108.

Projection system 108 (e.g., a quartz and/or CaF2 lens system or acatadioptric system comprising lens elements made from such materials,or a mirror system) is used to project the patterned beam received froma beam splitter 118 onto a target portion 120 (e.g., one or more dies)of substrate 114. Projection system 108 can project an image of thearray of individually controllable elements 104 onto substrate 114.Alternatively, projection system 108 can project images of secondarysources for which the elements of the array of individually controllableelements 104 act as shutters. Projection system 108 can also comprise amicro lens array (MLA) to form the secondary sources and to projectmicrospots onto substrate 114.

Source 112 (e.g., an excimer laser, or the like) produces a beam ofradiation 122. Beam 122 is fed into an illumination system (illuminator)124, either directly or after having traversed conditioning device 126,such as a beam expander 126, for example. Illuminator 124 can comprisean adjusting device 128 that sets the outer and/or inner radial extent(commonly referred to as σ-outer and σ-inner, respectively) of theintensity distribution in beam 122. In addition, illuminator 124 caninclude various other components, such as an integrator 130 and acondenser 132. In this way, beam 110 impinging on the array ofindividually controllable elements 104 has a desired uniformity andintensity distribution in its cross-section.

In one example, source 112 is within the housing of lithographicprojection apparatus 100 (as is often the case when source 112 is amercury lamp, for example). In another example, source 112 is remotelylocated with respect to lithographic projection apparatus 100. In thislatter example, radiation beam 122 is directed into apparatus 100 (e.g.,with the aid of suitable directing mirrors (not shown). This latterscenario is often the case when source 112 is an excimer laser. It is tobe appreciated that both of these scenarios are contemplated within thescope of the present invention.

Beam 110 subsequently interacts with the array of individuallycontrollable elements 104 after being directed using beam splitter 118.In the example shown, having been reflected by the array of individuallycontrollable elements 104, beam 110 passes through projection system108, which focuses beam 110 onto a target portion 120 of substrate 114.

With the aid of positioning device 116, and optionally interferometricmeasuring device 134 on abase plate 136 that receives interferometricbeams 138 via beam splitter 140, substrate table 106 is movedaccurately, so as to position different target portions 120 in a path ofbeam 110.

In one example, a positioning device (not shown) for the array ofindividually controllable elements 104 can be used to accurately correctthe position of the array of individually controllable elements 104 withrespect to the path of beam 110, e.g., during a scan.

In one example, movement of substrate table 106 is realized with the aidof a long-stroke module (course positioning) and a short-stroke module(fine positioning), which are not explicitly depicted in FIG. 1. Asimilar system can also be used to position the array of individuallycontrollable elements 104. It will be appreciated that beam 110 mayalternatively/additionally be moveable, while substrate table 106 and/orthe array of individually controllable elements 104 may have a fixedposition to provide the required relative movement.

In another example, substrate table 106 may be fixed, with substrate 114being moveable over substrate table 106. Where this is done, substratetable 106 is provided with a multitude of openings on a flat uppermostsurface. A gas is fed through the openings to provide a gas cushion,which supports substrate 114. This is referred to as an air bearingarrangement. Substrate 114 is moved over substrate table 106 using oneor more actuators (not shown), which accurately position substrate 114with respect to the path of beam 110. In another example, substrate 114is moved over substrate table 106 by selectively starting and stoppingthe passage of gas through the openings.

Although lithography apparatus 100 according to the invention is hereindescribed as being for exposing a resist on a substrate, it will beappreciated that the invention is not limited to this use and apparatus100 maybe used to project a patterned beam 110 for use in resistlesslithography, and for other applications.

The depicted apparatus 100 can be used in at least one of four modes:

-   -   1. Step mode: the entire pattern on the array of individually        controllable elements 104 is projected during a single exposure        (i.e., a single “flash”) onto a target portion 120. Substrate        table 106 is then moved in the x and/or y directions to a        different position for a different target portion 120 to be        irradiated by patterned beam 110.    -   2. Scan mode: essentially the same as step mode, except that a        given target portion 120 is not exposed in a single “flash.”        Instead, the array of individually controllable elements 104        moves in a given direction (e.g., a “scan direction,” for        example, the y direction) with a speed v, so that patterned beam        110 is caused to scan over the array of individually        controllable elements 104. Concurrently, substrate table 106 is        simultaneously moved in the same or opposite direction at a        speed V=Mv, in which M is the magnification of projection system        108. In this manner, a relatively large target portion 120 can        be exposed, without having to compromise on resolution.    -   3. Pulse mode: the array of individually controllable elements        104 is kept essentially stationary, and the entire pattern is        projected onto a target portion 120 of substrate 114 using        pulsed radiation system 102. Substrate table 106 is moved with        an essentially constant speed, such that patterned beam 110        scans a line across substrate 106. The pattern on the array of        individually controllable elements 104 is updated as required        between pulses of radiation system 102, and the pulses are timed        such that successive target portions 120 are exposed at the        required locations on substrate 114. Consequently, patterned        beam 110 can scan across substrate 114 to expose the complete        pattern for a strip of substrate 114. The process is repeated        until complete substrate 114 has been exposed line by line.    -   4. Continuous scan mode: essentially the same as pulse mode        except that a substantially constant radiation system 102 is        used and the pattern on the array of individually controllable        elements 104 is updated as patterned beam 110 scans across        substrate 114 and exposes it.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

Exemplary Alignment System

FIGS. 2 and 3 show alignment and focusing portions 250 and 350,according to various embodiments of the present invention. Alignment andfocusing portions 250 or 350 can be used additionally or alternativelyto those portions discussed above as performing similar operations inlithography tool 100. Through use of these portions 250 or 350, bothsurface layer and intermediate layer (e.g., up to about 150 μm deep)alignment patterns can be detected and utilized in aligning an objectfor subsequent feature pattern formation, as is discussed in more detailbelow. In one example, the object comprises material that allowsinfrared light to be transmitted and visible light to be reflected. Forexample, the object can be made from a silicon material, such as asemiconductor wafer, a flat panel display substrate, or any materialthat allows transmission of IR light.

Alignment and focusing portion 250 comprises alignment system 252 andfocusing system 254. Focusing system 254 is coupled to an object 214 andalignment system 252. In one embodiment, focusing system 254 includes anoptical system 256. In another embodiment, focusing system 254 includesoptical system 256 and a positioning system 258. In this latterembodiment, positioning system 258 is coupled to one or both of object214 and alignment system 252 to move one or both relative to opticalsystem 256, i.e., towards or away from optical system 256. This is doneto allow for fine tuning of co-focusing of visible and infrared light,as discussed in more detail below.

In one example, object 214 includes a support layer 260 and one or morelayers 262 (e.g., surface and intermediate layers), which include areasfor alignment patterns 264 and feature patterns 266. In another example,alignment patterns can be located on a back surface of object 214.

Turning now to FIG. 3, alignment system 252 in alignment and focusingportion 350 includes one or more light sources 370 (e.g. for visiblelight detection), one or more light sources 372 (e.g., for IR lightdetection), and one or more detectors 374. Each detector detects bothvisible and infrared light. For example, detectors 374 can be one ormore cameras, CCD sensors, CMOS sensors, or the like. It is to beappreciated a number of light sources 370/372 and detectors 374 cancorrelate, or a single detector 374 and multiple light sources 370/372,or vice versa, can be used. Also, as stated above, the light source caneither be placed in front of or behind the object 214 to allow foreither transmitted or reflected IR light. All permutations andvariations are contemplated within the scope of the present invention.

In the example shown in FIG. 3, object 214 includes a surface layer 262Aand an intermediate layer 262B. Each layer 262A and 262B includes one ormore respective alignment patterns 264A and 264B and respective featurepatterns 266A and 266B.

In one example, visible light 376 from one or more visible light sources370 is reflected from one or more alignment patterns 264A on surfacelayer 262A and infrared light 378 from one or more infrared lightsources 372 is transmitted through one or more alignment patterns 264Bon intermediate layer 262B or alignment pattern 264B on backside ofobject 214. Optical system 256 co-focuses the reflected visible light376 and the transmitted infrared light 378 onto a respective detector374. Each respective detector 374 generates a measured signal from thedetected visible light 376 and infrared light 378. The measured signalgenerated by detectors 374 are used to align object 214 for subsequentfeature pattern formation.

In one example, positioning system 258 is used to allow for co-focusingor further adjust or fine adjust a focal position or focal lengthbetween optical system 256 and detector 374 of visible light 376 and/orinfrared light 378, such that both wavelengths of light are co-focusedonto detector 374 within a desired tolerance.

Thus, in alignment and focusing portion 350, both alignment patterns264A and 264B are used in order to determine feature pattern positionson both of layers 262A and 262B. This dual-detection operation increasesalignment accuracy compared to only being able to detect an alignmentpattern on a surface layer of an object in conventional devices.

One exemplary environment for one or more embodiments of the presentinvention is in a Micralign lithography tool manufactured by ASML ofVeldhoven, The Netherlands. Example aspects of the Micralign lithographytool can be found in U.S. Pat. Nos. 4,068,947, 4,650,315, 4,711,535, and4,747,678, which are all incorporated by reference herein in theirentireties.

FIGS. 4 and 5 show two optical devices 456 and 556 that can be used inconjunction with each other in optical system 256, according to oneembodiment of the present invention.

With reference to FIG. 4, optical device 456 includes first, second, andthird lenses 480, 482, and 484. The triplet lens design provides anoptical prescription that allows focusing of visible and IR wavelengthsonto a same plane together.

In one example, lenses 480, 482, and 484 have the followingcharacteristics, whose parameters can actually be more or less thanshown depending on desired tolerances:

-   -   First lens 480 comprises R1=−64 to −65 mm, R2=−71 to −72 mm,        thickness≦1.5 to 1.6 mm, diameter, =22.0 mm, and a glass type is        SF10 (Schott);    -   Second lens 482 comprises R1=−71 to −72 mm, R2=15 to 16 mm,        thickness≦1 to 2 mm, diameter=22.0 mm, and a glass type is        N-PSK3 (Schott); and    -   Third lens 484 comprises R1=15 to 16 mm, R2=−35 to −36 mm,        thickness≦10 to 11 mm, diameter=22.0 mm, and a glass type is        N-PK51 (Schott).

In another example, lenses 480, 482, and 484 have the followingcharacteristics, whose parameters can actually be more or less thanshown depending on desired tolerances:

-   -   First Lens 480: R1=−64.795 mm, R2=−71.20 mm, thickness≦1.518 mm,        diameter, =22.0 mm. Glass type is SF20 (Schott)    -   Second Lens 482: R1=−71.20 mm, R2=15.469 mm, thickness≦1.5 mm.,        diameter=22.0 mm. Glass type is N-PSK3(Schott)    -   Third Lens 484: R1=15.469 mm, R2=−35.382 mm, thickness≦10.083        mm, diameter=22.0 mm Glass type is N-PK51 (Schott)

With reference to FIG. 5, optical device 556 includes first and secondlenses 586 and 588. The doublet lens design provides an opticalprescription that allows focusing of visible and IR wavelengths onto asame plane together.

In one example, lenses 586 and 588 have the following characteristics,whose parameters can actually be more or less than shown depending ondesired tolerances:

-   -   First lens 586 comprises R1=−26 to −27 mm, R2=infinity,        thickness≦3 mm, diameter=12 to 13 mm, and a glass type is BK7        (Schott);    -   Second lens 588 comprises R1=infinity, R2=−59 to −60 mm,        thickness≦5 mm, diameter=12 to 13 mm, and a glass type is F2        (Schott).

In another example, lenses 586 and 588 have the followingcharacteristics, whose parameters can actually be more or less thanshown depending on desired tolerances:

First Lens 586: R1=−26.697 mm, R2=infinity, thickness≦3 mm,diameter=12.7 mm Glass type is BK7 (Schott)

-   -   Second Lens 588: R1=infinity, R2=−59.03 mm, thickness≦5 mm,        diameter=12.7 mm. Glass type is F2 (Schott).

Exemplary Optical Path

FIG. 6A shows an optical arrangement 680 in a lithography system,according to one embodiment of the present invention. For exampleoptical arrangement 680 can be found in system 100. FIG. 6B shows anoptical system 682 of arrangement 680, according to one embodiment ofthe present invention.

With reference to FIG. 6A and with respect to visible light, visiblelight from a broadband light source 672 is directed to alignment marks664 on a substrate 614. Light reflecting from alignment marks 664 isdirected onto a detector 674 using an optic 686, for example a foldingmirror or the like. Additionally or alternatively, another optic 556 canbe placed between optic 686 and detector 674, for example a Barlowoptic.

With reference to FIG. 6A and with respect to IR light, IR light from alight source 672 is directed (e.g., via a filter) through optical system682, e.g., an IR optical system, via a waveguide or fiber optic device688. The IR light directed from optical system 682 is reflected fromalignment marks 664 and received back at optical system 682. Thereceived reflected IR light is directed from optical system 682 throughobjective lenses 680 and F-stop/aperture 692 onto folding mirror 694. Insome examples, multiple folding mirrors 694 can be used. Once reflectedfrom folding mirror 694, IR light is received at a field splitting optic696, e.g., a field splitting prism. From field splitting prism 696, theIR light travels via a reflecting optical device 698 and an opticssystem 456, which includes first and second lenses of differentmagnifying powers to reflecting optic 686. Depending on magnificationneed, light may travel through only one of the lenses. Then the lighttravels to reflecting optic 686. From reflecting optic 686, IR light isdirected onto detector 674, in one example through optic 687.

With reference now to FIG. 6B, an exemplary arrangement of opticalsystem 682 is shown. In this example, optical system 682 includes a beamsplitter 683, a blocking device 685, an annular mirror 687, and afocusing optic 689, e.g. a focusing lens. Blocking device 685 has atransparent peripheral portion 685A and an opaque central portion 685B,at least with respect to IR light. IR light received from opticalwaveguide 688 is reflected from beam splitter 683 through transparentportion 685A of blocking device 685 to be reflected from annular mirror687. After reflection, the IR light is transmitted back throughtransparent portion 685A of blocking device 685 and beam splitter 683before being focused onto alignment areas 664 on substrate 614. Afterreflecting from alignment areas 664, the IR light is reflected from beamsplitter 683 to travel as discussed above from optical system 682 todetector 674.

Exemplary Operation

FIG. 7 shows a flowchart depicting a method 700, according to oneembodiment of the present invention. In one example, method 700 iscarried out using one or more of the devices and/or systems describedabove. In step 702, at least visible light and infrared light aregenerated. In step 704, the visible light is reflected from a firstalignment pattern on a surface layer of an object. In step 706, thereflected visible light is focused onto a detector. In step 708, theinfrared light is transmitted through a second alignment pattern on asecond layer of the object, the second layer of the object being belowthe first layer of the object. In step 710, the transmitted infraredlight is focused onto the detector. In step 712, an alignment signal isgenerated based on the detected first and second alignment patterns. Instep 714, the object is aligned to receive a subsequent section of afeature pattern based on the generated alignment signal.

Exemplary Measured Alignment Patterns

Thus, according to one or more embodiments and/or examples of thepresent invention, discussed above, embedded wafer targets in IR or NIR(Near Infra Red) (hereinafter, NIR) and aligning mask targets in visiblelight spectrum are detectable substantially simultaneously orindividually using one camera. In some examples, this can be done withtwo separate cameras. However, in this example additional opticalcomponents would be needed.

In a first example, this was accomplished by changing opticalcharacteristics of specific optical element in the view path (e.g.,element 456) in terms of its radii. This allows viewing of the targetimage in visible and near IR wavelength at the same focal position orwithin the available depth of focus.

In a second example, this can be achieved if a chuck that carries asubstrate can be moved in a Z-direction. The focal position of theembedded alignment target is brought into a focal plane of the camera inIR first. This captures the image position information, which can bestored in memory, as would become apparent to one of ordinary skill inthe art upon reading and understanding this invention. Then, the systemretracts the chuck to its normal position, so that the aligning maskimage (projected on top of the substrate plane) comes into the focalposition of the camera, which X-Y location can be stored in memory. In asubsequent step, a fine alignment system can determine the offsetbetween these two recorded image positions and determine necessarycommands for alignment. This would substantially eliminate opticalmodifications in the viewing optics. However, it can require a controlsystem of the machine that controls chuck movement in a z-direction tobe modified.

While this second example allows IR alignment without any optical designchanges, it can require additional parameters to be taken intoconsideration. First, the complete alignment sequence requires twodistinct steps for collecting substrate and pattern generator targetpattern position data. Thus, by moving the chuck twice for eachsubstrate, an overall alignment time for alignment will be considerablylarger then needed for the first example. Since the substrate is mountedon chuck that is set in best lithographic focus (in x, y and zdirection) every time it is moved from that position, it is important toensure that this best focus position is maintained or repeated foroptimum lithographic performance.

In a third example, a same two step functionality can be achieved bymoving a camera in the z-direction under electronically controlledmotion. Then, at one time it will have an embedded substrate target inIR in focus with IR wavelength and the aligning pattern generator targetin focus with a visual wavelength for alignment. This example takes awaythe focus repeatability limitations in the second example, but requiresmore time per wafer for alignment.

Conclusion

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be apparent to persons skilledin the relevant art that various changes in form and detail can be madetherein without departing from the spirit and scope of the invention.Thus, the breadth and scope of the present invention should not belimited by any of the above-described exemplary embodiments, but shouldbe defined only in accordance with the following claims and theirequivalents.

It is to be appreciated that only the Detailed Description section ismeant to be used in interpreting claim limitations, and the Summary andAbstract sections are not to be used when interpreting the claimlimitations. The Summary and Abstract sections are merely one or moreexemplary embodiments or/examples of the present invention, while theDetailed Description provides additional/alternative embodiments and/orexamples.

1. A system, comprising: an alignment system including first and secondlight sources and a detector that generates a measured signal therefrom;an object, including, a first layer including a first alignment pattern,and a second layer including a second alignment pattern, the secondlayer being below the first layer; and a focusing system that co-focuseson the detector light from the first and second light sources after eachhas impinged on the respective the first and second alignment patterns,whereby the object is aligned based on the measured signal and whereinthe measured signal is generated from the co-focused light from thefirst and second alignment patterns.
 2. The system of claim 1, whereinthe focusing system comprises: an optical system positioned between theobject and the detector, wherein the optical system performs theco-focusing the light from the at least the first and second lightsources onto the detector.
 3. The system of claim 2, wherein thefocusing system further comprises: a positioning system that receivesthe measured signal from the alignment system and that moves at leastone of the object and the detector relative to the optical system basedon the measured signal, such that the light from the at least first andsecond light sources are co-focused on the detector.
 4. The system ofclaim 2, wherein the optical system comprises an optical elementincluding at least first, second, and third lenses.
 5. The system ofclaim 4, wherein: the first lens comprises R1=−64 to −65 mm, R2=−71 to−72 mm, thickness≦1.5 to 1.6 mm, diameter,=22.0 mm, and a glass type isSF20 (Schott); the second lens comprises R1=−71 to −72 mm, R2=15 to 16mm, thickness≦1 to 2 mm, diameter=22.0 mm, and a glass type isN-PSK3(Schott); and the third lens comprises R1=15 to 16 mm, R2=−35 to−36 mm, thickness=10 to 11 mm, diameter=22.0 mm, and a glass type isN-PK51 (Schott).
 6. The system of claim 5, wherein: the first lenscomprises R1=−64.795 mm, R2=−71.20 mm, thickness=1.518 mm,diameter,=22.0 mm, and a glass type is SF20 (Schott); the second lenscomprises R1=−71.20 mm, R2=15.469 mm, thickness=1.5 mm, diameter=22.0mm, and a glass type is N-PSK3 (Schott); and the third lens comprisesR1=15.469 mm, R2=−35.382 mm, thickness≦10.083 mm, diameter=22.0 mm, anda glass type is N-PK51 (Schott).
 7. The system of claim 2, wherein theoptical system comprises an optical element including at least first andsecond lenses.
 8. The system of claim 7, wherein: the first lenscomprises R1=−26 to −27 mm, R2=infinity, thickness≦3 mm, diameter=12 to13 mm, and a glass type is BK7 (Schott); the second lens comprisesR1=infinity, R2=−59 to −60 mm, thickness≦5 mm, diameter=12 to 13 mm, anda glass type is F2 (Schott).
 9. The system of claim 8, wherein: thefirst lens comprises R1=−26.697 mm, R2=infinity, thickness≦3 mm,diameter=12.7 mm, and a glass type is BK7 (Schott); the second lenscomprises R1=infinity, R2=−59.03 mm, thickness≦5 mm, diameter=12.7 mm,and a glass type is F2 (Schott).
 10. The system of claim 1, wherein: thefirst light source is configured to generate visible light that is usedto detect a position of the first alignment pattern; and the secondlight source is configured to generate infrared light that is used todetect a position of the second alignment pattern.
 11. The system ofclaim 10, wherein: the visible light is reflected from the firstalignment pattern before being focused onto the detector using thefocusing system; and the infrared light is transmitted through thesecond alignment pattern before being focused onto the detector usingthe focusing system.
 12. The system of claim 1, wherein: the light fromthe first light source is generated from a first side of the object; andthe light from the second light source is generated from a second sideof the object, opposite the first side.
 13. A method, comprising: (a)generating at least a first light beam and a second light beam; (b)impinging the first light beam onto a first alignment pattern on a firstlayer of an object; (c) focusing the impinged first light beam onto adetector; (d) impinging the second light beam onto a second alignmentpattern on a second layer of the object, the second layer of the objectbeing below the first layer of the object; (e) focusing the impingedsecond light beam onto the detector; (f) generating an alignment signalbased on the detected first and second alignment patterns; and (g)aligning the object to receive a subsequent portion of a feature patternbased on step (f).
 14. The method of claim 13, wherein the first andsecond light beams are focused onto the detector substantiallysimultaneously.
 15. The method of claim 13, wherein first light beam isvisible light and the second light beam is infrared light.
 16. Themethod of claim 15, wherein: the visible light beam is reflected fromthe first alignment pattern before being focused onto the detector; andthe infrared light beam is transmitted through the second alignmentpattern before being focused onto the detector.
 17. The method of claim13, wherein: the first light beam is generated from a first side of theobject; and the second light beam is generated from a second side of theobject, opposite the first side.
 18. A flat panel display formed usingthe method of claim
 13. 19. An integrated circuit formed using themethod of claim
 13. 20. A system, comprising: means for generating atleast a first light beam and a second light beam; means for impingingthe first light beam onto a first alignment pattern on a first layer ofan object; means for focusing the impinged first light beam onto adetector; means for impinging the second light beam onto a secondalignment pattern on a second layer of the object, the second layer ofthe object being below the first layer of the object; means for focusingthe impinged second light beam onto the detector; means for generatingan alignment signal based on the detected first and second alignmentpatterns; and means for aligning the object to receive a subsequentportion of a feature pattern based on the alignment signal.